Neuropeptide Y increases differentiation of human olfactory receptor neurons through the Y1 receptor

The olfactory bulb: A neuroendocrine spotlight on feeding and metabolism

Olfaction is the most ancient sense and is needed for food-seeking, danger protection, mating and survival. It is often the first sensory modality to perceive changes in the external environment, before sight, taste or sound. Odour molecules activate olfactory sensory neurons that reside on the olfactory epithelium in the nasal cavity, which transmits this odour-specific information to the olfactory bulb (OB), where it is relayed to higher brain regions involved in olfactory perception and behaviour. Besides odour processing, recent studies suggest that the OB extends its function into the regulation of food intake and energy balance. Furthermore, numerous hormone receptors associated with appetite and metabolism are expressed within the OB, suggesting a neuroendocrine role outside the hypothalamus. Olfactory cues are important to promote food preparatory behaviours and consumption, such as enhancing appetite and salivation. In addition, altered metabolism or energy state (fasting, satiety and overnutrition) can change olfactory processing and perception. Similarly, various animal models and human pathologies indicate a strong link between olfactory impairment and metabolic dysfunction. Therefore, understanding the nature of this reciprocal relationship is critical to understand how olfactory or metabolic disorders arise. This present review elaborates on the connection between olfaction, feeding behaviour and metabolism and will shed light on the neuroendocrine role of the OB as an interface between the external and internal environments. Elucidating the specific mechanisms by which olfactory signals are integrated and translated into metabolic responses holds promise for the development of targeted therapeutic strategies and interventions aimed at modulating appetite and promoting metabolic health.

Orexin-A increases the differentiation of human olfactory sensory neurons through orexin receptor type 1

Introduction

Sensorineural olfactory dysfunction significantly impairs the life quality of patients but without effective treatments to date. Orexin is a neurotrophic factor activates neuronal network activity. However, it is still unknown whether orexin can promote differentiation in human olfactory sensory neurons (OSNs). This study seeks to explore the impact of orexin on the differentiation of human olfactory neuroepithelial cells (HONCs).

Methods

The primary olfactory epithelium cells were cultured with or without orexin-A. The neural maturation-related and functional proteins were analyzed through immunofluorescence staining and Western blot. The function of HONCs were evaluated through the synaptic vesicle recycling assay.

Results

The results showed that HONCs in the orexin-A group expressed higher levels of stage-specific markers, including achaete-scute homolog 1, βIII-tubulin, and olfactory marker protein. Additionally, more components of signaling transduction pathways compared to the control group. The orexin-A-mediated differentiation of OSN effect can be nullified with dual orexin receptor antagonist suvorexant and the selective orexin receptor type 1 antagonist SB674042, instead of selective orexin receptor type 2 antagonist TCS-OX2-29.

Conclusions

Orexin-A elevates the expression of protein markers in human olfactory neuronal progenitor cells to stimulate the differentiation of OSN and enhances the formation of components of the olfactory-specific signaling transduction pathway via orexin receptor type 1.

Regeneration of olfactory neuroepithelium in 3-methylindole-induced anosmic rats treated with intranasal chitosan

Olfactory dysfunction significantly impairs the life quality of patients but without effective treatments to date. The previous report has demonstrated that chitosan mediates the differentiation of olfactory receptor neurons (ORNs) through insulin-like growth factors and insulin-like growth factor binding protein-2 axis in an in vitro model. However, whether chitosan can further treat olfactory dysfunction in vivo remains unexplored. This study aims to evaluate the therapeutic effect of chitosan on a 3-methylindole-induced anosmic rat model. Intraperitoneal injection of 3-methylindole is performed to induce anosmia in rats. Experimental results demonstrate that the food-finding duration after chitosan treatment gradually decrease to around 80 s, and both the olfactory neuroepithelium (ON) thickness and mature ORNs (expressing olfactory marker protein) are significantly restored. Furthermore, proliferating cells (expressing bromodeoxyuridine) are mainly co-expressed with immature ORNs (expressing βIII tubulin) below the intermediate layer of the ON in the chitosan-treated group on day 28 following 3-methylindole treatment. Conversely, proliferating cells are scattered over the ON, and co-localized with immature ORNs and sustentacular cells (expressing keratin 18) in the sham group, and even immature ORNs go into apoptosis (expressing DNA fragmentation and cleaved caspase-3), possibly causing incomplete regeneration. Consequently, chitosan regenerates the ON by regulating olfactory neural homeostasis and reducing ORN apoptosis, and serves as a potential therapeutic intervention for olfactory dysfunction in the future.